The invention provides a hydraulic controller for a continuously variable transmission according to the independent claims. DE 195 19 162 A1 makes known a hydraulic controller for a continuously variable transmission, especially for a twin V-pulley belt wrap transmission. It is used preferably during a failure of the electrical power supply to an electrohydraulic controller of the continuous transmission. The hydraulic controller has a pump for acting upon the delivery chambers of a first and second adjusting device for altering the transmission ratio of the transmission. A means is provided to control the pressure in the delivery chamber of the first adjusting device in the form of a valve that can be controlled by way of a pressure drop created at a throttle position. In the first control position, the valve connects the delivery chamber of the first adjusting device with the pump by way of a line installed after the valve.
The effective surface of the delivery chamber of the first adjusting device is greater than the effective surface of the delivery chamber of the second adjusting device. If the valve for controlling the pressure in the delivery chamber of the first adjusting device has been shifted through entirely, the same pressure is present in both delivery chambers. The greater resultant compressive force therefore occurs at the first adjusting device. As a result, the transmission ratio of the transmission tends to increase, i.e., to step up. As a result, the engine speed either decreases while the vehicle speed remains the same, or the vehicle speed increases while the engine speed remains the same. Certain intermediate values are also possible.
The pressure drop created at the throttle position is basically proportional to the engine speed. If the engine revs up, the pressure drop is high. The valve shifts through and the gear ratio becomes smaller. If the pressure drop decreases at a low engine speed, the pressure escapes through the valve for emergency operation, and the gear ratio of the transmission increases. The smallest gear ratio of the transmission is referred to here as xe2x80x9clowxe2x80x9d, and the largest is referred to as xe2x80x9coverdrivexe2x80x9d.
If the vehicle is shifted into neutral during rapid forward driving, the clutch is disengaged automatically. The engine speed can also decrease as a result. The valve shifts thereby in such a way that the pressure in the delivery chamber of the first adjusting device decreases and the resultant compressive force becomes smaller than the compressive force in the delivery chamber of the second adjusting device. The gear ratio of the transmission is adjusted to xe2x80x9clowxe2x80x9d. If the vehicle is now shifted from neutral into forward driving again, the clutch engages. Since the gear ratio of the transmission is at xe2x80x9clowxe2x80x9d, the input shaft then turns much more quickly than the output shaft. As a result, the engine speed increases rapidly. This can lead to mechanical damage and pose a risk to safety, and the vehicle passengers perceive it as being uncomfortable, because the vehicle decelerates abruptly.
Moreover, only one pump is provided in this hydraulic controller, which supplies the delivery chambers of the adjusting devices on the one hand and, on the other, is used for the valves of the hydraulic controller. For this reason, a high-pressure pump must be provided in order to perform both functions. Since higher pressures are therefore produced, especially at the control inputs of the valves, this leads to high leakage rates. In addition, this also results in increased fuel consumption.
Moreover, WO 97/34093 discloses a hydraulic controller that includes a means in the form of a valve having a first shift position in the forward driving operating state for an adjustment of the transmission in the xe2x80x9coverdrivexe2x80x9d direction. The transmission can only be adjusted in the xe2x80x9clowxe2x80x9d direction by way of an additional switching position, whereby, however, the valve becomes more complex and, therefore, more expensive. If this valve is located in the neutral operating state, the result is that the transmission moves into the xe2x80x9coverdrivexe2x80x9d transmission ratio. Means for preventing an adjustment in the xe2x80x9clowxe2x80x9d direction, which also means that the gear ratio remains constant, are not provided.
The hydraulic controller according to the invention and according to the independent claims has the advantage, on the other hand, that, after shifting from the forward driving or, possibly, the reverse operating state into the neutral operating state at least, especially during rapid driving, an undesired adjustment of the transmission to xe2x80x9clowxe2x80x9d is avoided entirely or at least to the greatest extent, and that the transmission can be adjusted in the xe2x80x9coverdrivexe2x80x9d and xe2x80x9clowxe2x80x9d directions in one shift position in the forward driving operating state.
This can be achieved especially easily by providing a shift valve, especially a manual shift valve, having four shift positions for the park P, reverse R, neutral N, and forward driving D operating states. It is advantageous hereby to ensure that, in the second control setting of the valve, the intermediate line at the port of the valve is connected with a drainage port of the valve, that the drainage port is connected by way of a line in which a throttle is preferably situated with a first port of the shift valve that is closed in the shift positions P and N and that is connected with a second port in the shift positions R and D which leads to a lower pressure level, e.g, a tank.
In a further design example, the port is closed in the second control setting of the valve, which makes an even simpler design possible. It is advantageous hereby if a branching line in which a throttle is preferably situated is connected to an intermediate line, which branching line is connected with a first port of the shift valve that is closed in the shift positions P and N and that is connected with a tank in the shift positions R and D by way of a second port.
According to a further design example, it is especially appropriate to connect a branching line to the intermediate line, which branching line is connected by way of a connecting line with the line that is installed after the throttle position in the delivery direction, and a throttle is to be situated in the connecting line. It is advantageous thereby if a line branches between the throttle and the throttle position that leads to a second control input of the valve. It is beneficial hereby to connect a line between the throttle and the throttle position that leads to a second port of the shift valve, which line is connected in the shift positions P, R and N with a first port to which a control line is connected that is connected with a third control input of the valve, and that the first port in the shift position D is connected with a tank port.
If the supply lines of the delivery chambers are connected with a pressure port of a pressure limiting valve, the pressurexe2x80x94especially in the delivery chamber of the second adjusting devicexe2x80x94can be adjusted in such a way that the means of transmission are not subjected to unnecessary wear.
It is advantageous if the throttle position is situated in a switch-over valve having two shift positions. In this design, a spring is provided at a first control input of the switch-over valve, and an electrical or hydraulic actuation is provided at its second control input. The switch-over valve includes, in an appropriate manner, a first pressure port and a first port that are connected with each other in the first shift position by way of the throttle position and, in the second shift position, by way of a basically pressure drop-free connection. It is advantageous to provide a first control line that is connected in the delivery direction before the switch-over valve and is connected with the first control input of the valve, and to situate a second control line in the delivery direction after the switch-over valve that is connected with the second control input of the valve.
A simple design is achieved hereby by connecting the second control line, which is installed in the delivery direction after the switch-over valve, with a second pressure port of the switch-over valve that is connected in the first shift position with a second port that is connected with the second control input of the valve by way of the control line. The second pressure port is thereby closed in the second shift position of the switch-over valve. Moreover, the switch-over valve includes a tank port that is closed in the first shift position and is connected with the second port in the second shift position.
For use in emergency operation it is advantageous if a branching line that is connected with the delivery chamber of the first adjusting device is connected to a third pressure port of the switch-over valve. The pressure port is connected with a third port in the first shift position and it is closed in the second shift position. The third port is connected hereby with the second control input of the pressure limiting valve by way of a line. In the second shift position of the switch-over valve, the third port is connected with the tank port of the switch-over valve.
If the throttle position is installed after a second pump that generates a lower pressure range than the at least first pumpxe2x80x94whereby it is appropriate for the first pump to be a high-pressure pump and for the second pump to be a low-pressure pumpxe2x80x94very low leakage rates occur in an advantageous manner. This also results in reduced fuel consumption.
It is appropriate if an additional pressure limiting valve is installed after the throttle position.
The hydraulic controller is simplified further if the valve for the emergency operation is also used for normal operation.
Further advantages and advantageous further developments of the hydraulic controller according to the invention arise out of the subclaims and the description.